Extension of phase modulation ellipsometry to measure refractive indices of liquid crystals

We present an extension of phase modulation ellipsometry to measure refractive indices in the visible and near infrared spectrum of multilayer and anisotropic structures, in particular liquid crystal cells, with arbitrary orientation of optical axis. An original software code was derived to process ellipsometer measurements, based on Jones formalism to express sinusoidal components of detected optical intensity reflected by a sample for different angles of the polariser and analyser respect to the sample orientation. In this way it is possible to obtain independent equations whose unknowns are the reflection matrix coefficients. Since it is possible only to obtain values of detected intensity and reflection coefficients given the refractive indices of the sample by using Berreman formalism, an algorithm has been developed to search best refractive index values which fit intensity measurements at each wavelength. Dispersion curves of refractive indices of 5CB have been obtained with accuracy of about 1%.